Expression of neuron specific phosphatase, striatal enriched phosphatase (STEP) in reactive astrocytes after transient forebrain ischemia

We studied the distribution and change of striatal enriched phosphatase (ST EP) in the gerbil hippocampus after transient forebrain ischemia. STEP was expressed in the perikarya and in neuronal processes; it was not detected i n nonneuronal cells of control animals. After 5-min forebrain ischemia, STE P immunoreactivity (STEP-IR) was preserved for 2 days; it disappeared 4 and more days after ischemia with completion of delayed neuronal death (DND) i n the CA1 subfield. Furthermore, only in the CA1 after ischemia, STEP was e xpressed in reactive astrocytes for 4 to 28 days, showing different pattern s of glial fibrillary acidic protein (GFAP)-positive reactive astrocytes. A fter non-or less-than lethal ischemia, STEP expression in reactive astrocyt es corresponded with the degree of neuronal degeneration. Immunoblot analys is of the CA1 subfield revealed the expression of three isoforms, STEP45, - 56 and -61; their expression patterns changed with time after ischemia. The se data suggest that neuronal STEP is preserved until cell degeneration aft er ischemia and that STEP is expressed in reactive astrocytes only after le thal ischemia, with different expression patterns for its isoforms. Of STEP 45, -56 and -61, STEP61 was the most strongly expressed in the reactive ast rocytes; both STEP45 and -61 were expressed in neurons and the expression o f STEP56 was weak. STEP may play an important role not only in neurons but also in reactive astrocytes after ischemia, depending on neuronal degenerat ion. (C) 2000 Wiley-Liss, Inc.